When an electro-static discharge (ESD) device is realized in a single substrate together with a semiconductor such as a metal-oxide semiconductor field-effect transistor (MOSFET), a normal contact is formed in the ESD device region, and a blanket contact is formed in the semiconductor region.
When forming the normal contact and the blanket contact by using a single mask, tetraethyl orthosilicate; Si(C2H5O4) and borophosphosilicate glass (BPSG) are sequentially deposited on the ESD device region and the semiconductor region to form a polysilicon-metal dielectric (PMD) layer. Thereafter, a pattern is formed in order to form the normal contact over an ESD poly. In this case, the region for the blanket contact does not require a pattern.
In the case of the normal contact, a trench having the shape of a wine glass is formed in order to perform a metal gap fill process. In this case, after performing an isotrophic etch process, an anisotrophic process is performed to form a trench having a desired profile. However, after the etch processes have been performed, a PMD layer may be excessively removed from the blanket contact although the PMD layer having a predetermined thickness is formed on the blanket contact. Accordingly, an insulating function is not achieved on the blanket contact. This phenomenon may occur by the following causes.
First, since the PMD layer is thicker in the ESD device region than in the semiconductor region due to difference between the contact structures, most of the PMD layer is removed from the semiconductor region in the etch processes. In other words, although the BPSG must be etched by about 1000 Å or less on a trench poly of the semiconductor region, the BPSG is etched from the trench poly by about 2000 Å or more due to thickness difference. Accordingly, the contact of the ESD device cannot be formed if the loss of the BPSG of the semiconductor region is maintained to about 1000 Å or less.
Second, in order to improve the contact property of the normal contact over the poly of the ESD device, an etch process must be sufficiently performed by using a mask. In contrast, in the case of the blanket contact of the semiconductor region, an etch process must be performed at an etch rate as low as possible such that the PMD layer over the trench poly is removed as little as possible. This causes a contradiction situation in the contact etch process.